Dumbledore has been too busy to step back and think about the situation creatively.
Dumbledore is making up a reason to invite Harry Potter into his office to (a) get his report on Lucius Malfoy, (b) warn Harry about the Dementor coming onto campus, (c) encourage Harry to practice his cunning outside the formalized exercises of Quirrell’s armies, (d) lend credence in Harry’s eyes to his suspicions of Quirrell by revealing that Quirrell is acting suspiciously, (e) query Harry about Voldemort.
Two possibilities:
Dumbledore has been too busy to step back and think about the situation creatively.
Dumbledore is making up a reason to invite Harry Potter into his office to (a) get his report on Lucius Malfoy, (b) warn Harry about the Dementor coming onto campus, (c) encourage Harry to practice his cunning outside the formalized exercises of Quirrell’s armies, (d) lend credence in Harry’s eyes to his suspicions of Quirrell by revealing that Quirrell is acting suspiciously, (e) query Harry about Voldemort.
I do not find either entirely implausible.
I agree with (2). I could quibble over the subpoints, but it comes down to: to get Harry’s reaction.